BACKGROUND: A well-defined rate of adverse events following cerebral angiography in patients with symptomatic intracranial atherosclerosis would be useful to physicians making decisions regarding imaging and treatment of these patients. We report the adverse events associated with angiography in patients who underwent single-vessel cerebral angiography as part of the study protocol in the Warfarin-Aspirin for Symptomatic Intracranial Arterial Stenosis trial.METHODS: Single-vessel cerebral angiography was performed to specifically define the degree of stenosis in 196 patients suspected of having intracranial atherosclerotic stenosis on noninvasive tests. Adverse events that occurred within 24 h of cerebral angiography were reported by the sites performing the angiography.RESULTS: Overall, neurological adverse events occurred in 4 patients (2.0%; 95% CI: 0.6-5.1%), and nonneurological adverse events occurred in 12 patients (6.1%; 95% CI: 3.2-10.5%). All of the neurological adverse events were transient.CONCLUSIONS: The risk of permanent neurological adverse events associated with single-vessel cerebral angiography in patients with symptomatic intracranial atherosclerosis is relatively low. The quantification of the risk of cerebral angiography in patients with intracranial atherosclerosis provides useful information to consider when evaluating noninvasive imaging techniques for their relative value.